Electric vehicles and hybrid electric vehicles require onboard batteries to power their electric drive systems. The performance requirements of such vehicles generally require combining a large number of batteries together to provide a sufficiently high voltage and current for powering the electric drive system. For example, Li-ion batteries can be stacked to produce battery packs or modules with very high voltage and current capabilities. In conventional electric or hybrid electric vehicles, such Li-ion batteries often are configured to generate voltages on the order of 400V DC.
Typically, in such vehicle applications, the battery voltage is applied to the drive system under control of a battery management system (BMS) electronic controller. Specifically, the battery is connected to the vehicle via a contactor or other type of switch element controlled by the BMS. Throughout the lifetime of the vehicle, it is possible that the contactors may fail or degrade, resulting in improper operation. Such contactor faults or failures can arise from the very large operating currents and transients that are typically conducted by the contactors during operation of the vehicle. For example, currents in electric vehicles can exceed 200A under some conditions. As a result, the switch elements used to connect the battery to the vehicle may become stuck open or closed under mechanical or electrical stress during operation.
When such contactor failures occur, it is generally desirable to generate control signals for the BMS such that the battery can be disabled to prevent further damage to the vehicle or to reduce the risk of injury to the driver or passengers of the vehicle. Further, it is generally desirable to generate signals such that service personnel can easily assess and repair the contactor failure.
Conventional methods for detecting the physical state of a contactor, a relay, or other types of switch elements in high voltage DC systems typically rely on coupling or injecting a waveform on a first side of a switch element and thereafter detecting the waveform on the second side of the switch element. However, such configurations typically require additional components and have additional power requirements.